Marine sponges produce a number of bioactive, bisindole metabolites containing either an imidazole- or a piperazine-derived linker unit. These compounds have received much attention due to their potent biological activities as antitumor, antiviral, and antiinflammatory agents. The bisindole alkaloid topsentin A 1 is representative of a class of deep-sea sponge bisindole metabolites that contain an imidazole linker. The nortopsentins, including nortopsentin B 2 and nortopsentin D 3, also are examples of bisindole sponge metabolites with an imidazole linker. The 2,5-bis(3′-indolyl)piperazine alkaloids, dragmacidin B 4 (from the sponge, Hexadella sp.) and 2,5-bis (6′-bromo-3′-indolyl)piperazine 5 (from the tunicate, Didemnum candidum) are representative of a group of bisindole metabolites containing a piperazine linker. Biosynthetically, dragmacidins and topsentins are conceivably derived by the condensation of two tryptamine derivatives in either a head-to-head (topsentins) or head-to-tail (dragmacidins) orientation. 
Previous syntheses of bis(indolyl)imidazoles have been accomplished via palladium-catalyzed cross coupling of 3-indolylboronic acids or 3-stannylindoles with halogenoimidazoles (See, for example, Kawasaki et al., J. Chem. Soc., Chem. Commun., 1994, 2085), rearrangement and dimerization of hydrazinium bromide prepared from 3-bromoacetylindole (See, for example, Braekman et al., Pure & Appl. Chem., 1989, 61, 509), and oxidative dimerization of 3-hydroxyacetylindoles using Cu(OAc)2 and NH4OH (See, for example, Tsugi, et al., J. Org. Chem. , 1998, 53, 5446).
Despite the broad range of biological activity exhibited by the class of bis(indolyl)piperazines, including cytotoxicity, only two reports have described the successful construction of the piperazine ring system (See, Witlock and Cava Tetrahedron Lett., 1994, 35, 371 and Jiang et al, J. Org. Chem., 1994, 59, 6823). In both reports, access to the substituted piperazines was achieved via diborane reduction of diketopiperazine intermediates.